Remove stems from mushrooms. Scrape gills with a small spoon to form small sides to help hold stuffing.

In a large sauté pan, sauté garlic, onions and red bell pepper in olive oil until onions are translucent and garlic is starting to turn golden color. Add sausage and sauté briefly. Rough chop spinach. Fold in and cook until wilted, about 2 to 3 minutes. Remove from heat and toss in Parmesan, salt and pepper. Divide mixture evenly and place in cleaned portobello mushrooms. Top each mushroom with ½ ounce slice fresh mozzarella.

Place mushrooms in baking pan and bake in oven for 25 minutes. Remove from oven and sprinkle each with 1 teaspoon parsley.